Crypto exchange Coinbase has halted all ethereum classic transactions withdrawals and deposits due to a series of blockchain history reorganizations on the network Ethereum classic saw more than 100 blocks reorganized during a 51 percent attack late Sunday according to at least two different block explorers Bitfly Etherchain and Blockscout Coinbase said in its blog post that it detected some 88 500 ETC being double-spent totaling some 460 000 Media publication Coinness reported Monday that an in-house analyst had detected an abnormal hash rate or computation energy going into a single mining pool potentially causing mass reorganizations reorgs of mined blocks Though initially refuted by the core proponents behind ethereum classic on Twitter the official account has now affirmed potential cause for concern tweeting out We are now working with Slow Mist and many others in the crypto community We recommend exchanges and pool significantly increase confirmation times SlowMist a China-based security firm first alerted users of the strange activity occurring on the network Monday morning stating that its team was trying to trace the cause of the attack SlowMist did not immediately respond to a request for comment Recent reports from Coinness stated that certain abnormality had been detected in the mining hash rate of a private ethereum classic mining pool Disputed accounts The duration of the attack seems to be in dispute Blockscout reported block reorganizations occurring at 02 00 UTC and 05 00 UTC Monday while Bitfly said in a Tweet at 17 00 UTC that the attack was potentially ongoing In its note Coinbase wrote that the attacks are ongoing Blockscout project lead Andrew Cravenho affirmed to CoinDesk that although the last recorded reorg attack was seen 14 hours ago the network is constantly fluctuating and people are always switching their hashing power suggesting the potential for continued disruption under the perfect circumstances He also noted that the reorg may have begun before being noted on Blockscout In a blog post Coinbase said it first noticed the reorg on Jan 5 two days before other reports began And though reiterating to CoinDesk that indeed a huge reorg took place on the ethereum classic blockchain Cravenhos explanation of the event as a 51 percent attack is not widely agreed upon In an email to CoinDesk ethereum classic dev advisor Cody Burns said that the activity could not be labeled a 51 percent attack but rather a selfish mining attack caused by a client-local phenomenon He added in a post on Twitter that the entire Ethereum network doesnt reorganize simultaneously It would be more likely that someone discovered all of Coinbase ETC nodes and surrounded them In response to the deep reorg Kraken announced in an incident report that it was increasing the number of confirmations required to make an ethereum classic deposit Bitfly told CoinDesk that it was likewise taking this action Ethereum classic logo image via Shutterstock